A focused ion beam (FIB) device that includes a gas field ion source and uses hydrogen, helium, neon, or other gas ions is generally known. Unlike a gallium FIB from a frequently used liquid metal ion source, a gas FIB is a device that does not contaminate a sample with gallium. Further, the gas field ion source generates gas ions having a narrow energy width and is small in ion generation source size. Therefore, the gas field ion source is capable of forming a finer beam than a gallium liquid metal ion source.
Furthermore, the gas field ion source has an emitter, which emits ions, and an extraction electrode, which is disposed opposite the emitter, and emits ions by applying a voltage between the emitter and the extraction electrode. It is known that the performance of an ion source improves due, for instance, to an increase in the angular current density of the ion source when a micro-protrusion is formed on the apex of the emitter of the gas field ion source. It is also known that the micro-protrusion can be formed by sharpening the apex of a base part of the emitter, which is formed of single crystal tungsten, by means of field evaporation (refer, for instance, to Patent Literature 1). It is further known that the micro-protrusion can also be formed by using a second metal, which is different from a first metal used as the base part of the emitter (refer, for instance, to Patent Literature 2). In this case, a noble metal (e.g., iridium or platinum) is used as the second metal while tungsten is used as the first metal.
The micro-protrusion of the emitter breaks within a certain period of time as it is affected by an impurity gas in the gas field ion source. If the micro-protrusion of the emitter can be regenerated in the ion source, the phenomenon of such breakage does not limit the operational lifetime of the emitter so that the ion source can be used in a substantially continuous manner. Meanwhile, when a noble metal is used as the second metal, the micro-protrusion (pyramid structure) can be regenerated simply by heating as far as the noble metal remains undepleted.